The invention relates to a steering device for a motor vehicle with an actuating member for the introduction of the steering movement and with a steering linkage to transfer the steering movement to the wheels.
The known steering devices consist of a steering wheel which is rotatable by hand, which can be turned from stop to stop usually 3.5 to 4.5 revolutions and the rotary movement of which is transferred via a steering gear mechanically directly to a steering linkage, which brings about the angle of deflection of the steered wheels. Such steering devices have been in use in various forms since the start of the development of automobiles, more revolutions from stop to stop also being able to be provided in buses and lorries, apart from a larger diameter of the steering wheel, in order to improve the transmission ratios in favour of less expenditure of energy. In addition, in particular in passenger cars with front wheel drive, pneumatic steering aids are widely used as so-called power-assisted steering mechanisms.
The direct mechanical coupling between the steering wheel and the steered wheels indeed also has various disadvantages. Firstly, it can not be entirely avoided that unevenness in the roadway, despite intercalated damping devices, is transmitted as far as to the steering wheel as vibrations of greater or lesser intensity, which is not only uncomfortable but also leads to greater fatigue on longer journeys. A further disadvantage consists in that in the design of such steering devices from the outset a decision has to be made for a particular transmission ratio, in which one person finds fault with an insufficient contact with the roadway, whereas for another the same transmission ratio still requires too much power. In addition, the different requirements in driving straight ahead on the motorway on the one hand and when parking on the other hand can not be satisfactorily fulfilled in the conventional steering devices or can only be fulfilled with considerable technical expenditure.
In addition to this is the fact that in modern steering wheels, increasingly more actuating devices are arranged so that they can be reached without the hand having to be taken from the steering wheel. In conventional steering devices, the reliability of such actuations depends on the fact that the individual commands can be transferred reliably from the rotatable steering wheel to fixed parts of the bodywork. Also for this a whole range of proven technical solution possibilities in fact already exists, which, however, all have the remainder of a liability to breakdown and many of which are overloaded in the case of distinct increase to the actuating devices accommodated on the steering wheel.
The problem therefore exists of indicating a steering device of the type initially mentioned, in which the above-mentioned disadvantages can not occur, which can be easily adapted to the most varied of requirements and in which a plurality of levers and keys for the most varied purposes can be readily arranged on the actuating member, without the signal transmission presenting difficulties.
To solve this problem, a generic steering device is proposed, which is characterized in that the actuating member consists of a xe2x80x9csteering wheelxe2x80x9d rotatable about a small angle and of a measured value transmitter to generate an electrical or electronic position signal, and that the steering linkage is actuated by an adjustment drive, which is controllable by an electrical or electronic regulating device as a function of the position signal.
In the steering device according to the invention, the term xe2x80x9csteering wheelxe2x80x9d was continued to be used, although the actuating member is only still rotatable about a very small angle. Otherwise, however, it can be constructed largely as a conventional steering wheel. The mechanical uncoupling from the steering linkage and the transmission of the steering commands electrically or electronically is important. For this, a measured value transmitter is provided for generating an electrical position signal, which is supplied to an electrical or electronic regulating device, which in turn generates control commands, as a function of the position signal, for an adjustment drive which actuates the steering linkage.
The steering device according to the invention has the advantage that in the xe2x80x9csteering wheelxe2x80x9d which is only slightly rotatable, in a conventional manner an airbag and also actuating and display devices can be accommodated, without, as in a steering wheel which is rotatable several times through 360xc2x0, particular devices having to be provided for the transmission of the actuating or display signals from a fixed component to a component which is movable through several revolutions or vice versa.
The steering device according to the invention has in addition the great advantage that as a result of the mechanical uncoupling, in a very simple manner any desired transmission ratios can be realized, because in this respect one only has to take action on the software of the electronic regulating device. Moreover, it is readily possible to select a very direct transmission ratio for driving straight ahead on the motorway and to provide the opposite design range for parking operation.